*/
if (! ((Paper_column::is_musical (l_neighbor) || Item::is_breakable (l_neighbor))
&& (Paper_column::is_musical (r_neighbor) || Item::is_breakable (r_neighbor))))
*/
if (! ((Paper_column::is_musical (l_neighbor) || Item::is_breakable (l_neighbor))
&& (Paper_column::is_musical (r_neighbor) || Item::is_breakable (r_neighbor))))